Without limiting the scope of the present invention, its background is described with reference to constructing a subterranean well, as an example.
In conventional practice, the drilling of an oil or gas well involves creating a wellbore that traverses numerous subterranean formations. For a variety reasons, each of the formations through which the well passes is preferably sealed. For example, it is important to avoid an undesirable passage of formation fluids, gases or materials out of the formation and into the wellbore or for wellbore fluids to enter the formation. In addition, it is commonly desired to isolate producing formations from nonproducing formations to avoid contaminating one formation with the fluids from another formation.
To avoid these problems, conventional well architecture includes the installation of casing within the wellbore. In addition to providing the sealing function, the casing also provides wellbore stability to counteract the geomechanics of the formation such as compaction forces, seismic forces and tectonic forces, thereby preventing the collapse of the wellbore wall. In standard practice, each succeeding casing string placed in the wellbore has an outside diameter having a reduced size when compared to the previously installed casing string. Specifically, the wellbore is drilled in intervals whereby a casing, which is to be installed in a lower wellbore interval, must be passed through the previously installed casing string in an upper wellbore interval.
The casings are generally fixed within the wellbore by a cement layer between the outer wall of the casing and the wall of the wellbore. During the drilling of the wellbore, annuli are provided between the outer surfaces of the casings and the wellbore wall. When a casing string is located in its desired position in the well, a cement slurry is pumped via the interior of the casing, around the lower end of the casing and upwards into the annulus. As soon as the annulus around the casing is sufficiently filled with the cement slurry, the cement slurry is allowed to harden. The cement sets up in the annulus, supporting and positioning the casing and forming a substantially impermeable barrier which divides the wellbore into subterranean zones.
In one approach, each casing string extends downhole from the surface such that only a lower section of each casing string is adjacent to the wellbore wall. Alternatively, the wellbore casings may include one or more liner strings which do not extend to the surface of the wellbore but instead typically extend from near the bottom end of a previously installed casing downward into the uncased portion of the wellbore. Liner strings are typically lowered downhole on a work string that may include a running tool that attaches to the liner string. The liner string typically includes a liner hanger at its uphole end that is mechanically or hydraulically set. In one example, an expander cone is passed through the liner hanger to radially expand and plastically deform the liner hanger into sealing and gripping engagement with the previously installed casing string.
Preferably, the liner string is set or suspended by the liner hanger at a location in the wellbore so that the downhole end of the liner string extends to close proximity of the bottom of the wellbore. It has been found, however, that in certain wellbores such as deviated wellbores, horizontal wellbores, multilateral wellbores and the like, significant force is required to work the liner string to the bottom of the wellbore. Use of such significant force has resulted in certain liner hangers becoming prematurely set within the previously installed casing string when the lower end of the liner string is still remote from the bottom of the wellbore. Accordingly, a need has arisen for a setting tool that is operable to deliver the required force to work the liner string to the bottom of the wellbore without prematurely setting the liner hanger in the previously installed casing string.